Isomerization of paraffinic hydrocarbons



vMay 21, 1946. U. TSAO l IsoMERIzATIoN oF PARAFFINIC HYDRocARBoNs Filed Dec. l0, 1942 Patented May 21, 1946' UNITED STATES PATENT OFFICE ISOMERIZATION F PARAFFINIC HYDROCARBONS .Utah Tsao, New York, N. Y.. assignor to The Lummus Company, New York, N. Y., a corporationA of Delaware Application December-'1o. 1942, serial No. 468,495

Claims. (Cl. 26o-$83.5)

This invention` relates to an improvement in the conversion of hydrocarbons and particularly to an improved method for lcarrying out the isomerization of normal or slightly branched chain hydrocarbons to branched chain or more highly branched chain hydrocarbons in the presence of an aluminum halide catalyst such as aluminum chloride. It is especially useful in the isomerization of normal butane to isobutane.

The catalytic effect of the aluminum halides,

. particularly anhydrous aluminum "chloride, in

the conversion of various hydrocarbon materials to other and more desirable hydrocarbon products is well known. In the operation of such processes, a finely divided aluminum halide may be suspended in the hydrocarbon mixture to be converted; and the reaction may be carried out as a batch or as a continuous procedure, as desired, with subsequent separation lof the converted products from the catalyst. Such processes may also be conducted in such a way that the hydrocarbon reactants, generally in the vapor state, are brought into contact with the aluminum halide catalyst; in such case, the vapors are passed over the catalyst, which is suitably contained or supported in a, reactor or similar vessel. The catalyst either may be used by itself or may be deposited on an appropriate, preferably inert carrier.

Recently, the use of anhydrous aluminum chloride as a catalyst for various hydrocarbon conversions, particularly the isomerization of normal butane to isobutane, has attained considerable importance and has attracted Widespread attention. In thev operation of a continuous process utilizing this catalyst, however, several disadvantages generally arise to lower the efciency of the process. Because of its relatively high vapor pressure. aluminum chloride, although normally a solid, partially vaporizesbr sublimes under the conditions of reaction so that aluminum chloride vapors are carried oil. with the vaporous products of conversion. It is to be noted that aluminum chloride sublimesat approximately 183 C. under substantially atmospheric pressure. This vaporized aluminum chloride causes considerable Adiiiiculty in the. hydrocarbon vapor condenser; for, as the vaporous hydrocarbon products are condensed, the aluminum chloride vapors are likewise condensed and deposited on the condenser surface.

of aluminum chloride gradually increases until the condenser finally becomes so plugged that it must be shut down for cleaning.

As a result, the deposit- In addition, a-sludge comprising a complex reaction product of aluminum chloride and hydrocarbons is formed during the reaction. This sludge must be continuously removed from the process and replaced by fresh aluminum chloride in order that an effective degree of conversion can be maintained. Generally, however, this sludge dissolves or entrains a, small amount of still catalytically active aluminum chloride, which it is desirable to recover for maximum operating efliciency. It is to be noted that aluminum chloride is slightly soluble in Various hydrocarbons and in its hydrocarbon complex.

Accordingly, the primary object of my invention is to provide an improved. process wherein the above-noted disadvantages are substantially avoided.

A further object of my invention is the provision of an improved system for the separation. and recovery of entrained aluminum chloride vvapors from `vaporous hydrocarbon mixtures.

Another object ofv my invention is the provision of an improved system for recovering the active aluminum chloride entrained by the complex aluminum chloride-hydrocarbon sludge formed in aluminum chloride-catalyzed hydrocarbo conversions. v

A particular object of my invention is to propanying drawing showing a ilow sheet of one sysi tem for carrying out my invention.

For convenience only, my invention will be described in connection with the isomerization of normal butane to isobutane in the presence of anhydrous aluminum chloride as the catalyst although it is applicable to any vapor phase hydrocarbonl conversion system in which an aluminum halide. is used as the catalyst.

According to my invention, the isobutane conl version products are passed to a scrubber, wherein they are brought into contact with the aluminum chloride-hydrocarbon sludge, which acts to scrub out the entrained and vaporized aluminum chloride from the reaction products. The con-f version products, freed ofk catalyst vapors, are

fractionated for separation of the desired isobutane product. The sludge containing the sepgrated but sun active aluminum chloride incombined with similar sludge from the reactors and the resulting mixture is passed to a stripper..

wherein it is contacted with incoming normal butane charge vapors, which serve to strip the entrained or dissolved aluminum chloride from the sludge. The butane vapors now containing vaporized aluminum chloride are passed to the catalytic reactors, anda portion of the stripped sludge is then returned to the scrubber for reuse therein. v l

tion system is used in conjunction with an alkylation unit to provide the isobutane feed there-- for, this butane charge 'may comprise the normal two may be employed. The number. used debutane fraction separated from the alkylation y products in the alkylation unit. The incoming lbutane charge is generally introduced into the system under a pressure sufiicient to maintain it in liquid condition. A heater |2 is provided to vaporize this charge and to raise it to the necessary reaction temperature before it is brought into contact with the isomerization catalyst.

The vaporized butane is then passed through line Il into manifold I5 and into line l0. The portion passed through line I8 is conducted to stripper |8, wherein it countercurrently contacts the complex aluminum `chloride-hydrocarbon sludge formed during the isomerization reaction.

This sludge/.contains entrained particles of alu-l minum' chloride which is still catalytically active and which it is desirable to recover. As will be explained in greater detail hereinafter, this entrained aluminum chloride is stripped from the sludge by the incoming butane charge vapors. The butane vapors containing the stripped aluminum chloride are removed from stripper i8 through line 20 and are conducted to manifold I5 for introduction into the catalyst chambers or reactors 22 and 23. Prior to introduction into these reactors. the butane vapors are admixed with gaseous hydrocarbon chloride, which is recycled to the system through line 24. This hydrogen chloride acts as an accelerator or activator for the aluminum chloride catalyst and is necessary for the production of satisfactory yields of isobutane. The hydrogen chloride gas should be substantially anhydrous to prevent interference with the isomerization reaction. Desirably.

- it should comprise. about 7 mol per cent of the and the recycledhydrogen chloride, to the catalyst chambers or reactors 22 and 23 through lines 25 and 2B, respectively. These reactors contain the anhydrous aluminum halide catalyst, which preferably consists of pieces of solid aluminum chloride of suitable size. It is to be noted, however, Vthat the aluminum chloride catalyst may "also be supported on a suitable carrier, which may be inert or slightly catalytically active as desired. Although I have shown two catalytic reactors,1 only one may be provided. or more than pends on the desired' throughput of the isomerization unit since, when the solid'nonsupported aluminum chloride isl used as the catalyst, lthe butane charge vapors can be passed in parallel through all of the reactors and need not be alternately passed through the several reactors provided,

Within reactors 22 and 23, a substantial portion of the normal butane is isomerized to isobutane by the 4action `of the aluminum chloride thereon. These reactors may be desirably maintained at a temperature of about 190 F. and a pressure of about 165 lbs. per sq. in. gage. The

vaporous hydrocarbon conversion products in-l cluding the is'obutane formed are removed from reactors 22 and 23 through lines 21 and 28, respectively, 'into manifold 29, which conducts them through line to scrubber 3| for a purpose more fully described hereinafter.

During the isomerization reaction, the aluminum chloride tends to sublime .and also tends to form a. complex compound with the hydrocarbons undergoing conversion. Both of these characteristics of aluminum chloride result in a loss of catalyst, which must' be replaced from time to time in order to maintainl the desired throughput. The complex compound that is formed re-v sults in a sludge', which may be conveniently removed from reactors 22 and 23 through lines 82 and 33, respectively, intol manifold 3l. As

ride particles which 'are still catalytically active are entrained therein and are withdrawn therewith the hydrocarbon product vapors.

' recovered and returned to the catalyst reactors V for reuse in the process, and undue loss of cata-- lyst is avoided.

Because of the gradual` sublimation of the solid aluminum chloride during y the reaction, aluminum chloride vapors are carried on along This sublimation characteristic of the catalyst represents a material factor in the economic operation of the isomerization process and vwould account for a material operating loss ii it were not'counteracted. Accordingly, it is highly desirable to recover this entrained vaporized catalyst, not only for economic reasons, but also to prevent deposition of aluminum chloride in thesubsequent hydrocarbon vapor condensers with the consequent plugging of the condenser surface.

According to my invention, this vaporized alu-v minum chloride is separated from the hydrocarbon product vapors prior to condensation thereof by a novel method. As already noted, thse product vapors are introduced into scrubber 3| throughline 30.. Within scrubber 3|, these vapors flow upwardly and cuntercurrently contact a complex aluminum chloride-hydrocarbon sludge, which serves to substantially scrub the entrained aluminum chloride from the hydrocarbon product vapors. For this purpose, scrubber 3| is desirably filled with a suitable packing material 35, over which the aluminum chloride sludge downwardly vtrickles. This sludge is obtained from stripper` IB -and is passed therefrom bygravity to scrubber 3| .through line 38. Accordingly, this sludge is substantially free of or lean in entrained aluminum chloride particles portion of this uncondensed recycled hydrogenv lchloride gas is diverted from line 12 through line 13 and is passed to jet pump 14 (convenand, thus, forms an excellent scrubbing medium for the separation of the vaporized aluminum chloride from the isobutane product vapors.

The sludge containing thel separated aluminum chloride is removed from scrubber 3| through bottoms line 38 into the sludge pot 4|). Removal of this sludge is controlled by valve 4|, which is operated by the level of the sludge in the top of scrubber 3|. 'I'his sludge level is'desirably maintained above the top of the packing 35 so that an effective scrubbing action of the product vapors is continuously provided. The sludge is discharged from sludge pot 40 through line 42 into manifold 34 for recovery of the aluminum chloride contained therein.

The isobutane product 'vapors substantially freed of entrained aluminum chloride, are withdrawn from scrubber 3| through line 43 and are passed to separator 44, wherein any sludge that may be carried over with these vapors is sepai rated. Such separated sludge is removed through .lline 46 desirably into manifold 34. The product ,vapors are then passed through line 41 to condenser 48 for substantially complete condensajtion. There is relatively little danger that aluminum chloride will be deposited on the con- -densing surface of this condenser since it has been substantially completely removed by the scrubhing action of the sludge in scrubber 3|. If desired, however, the hydrocarbon vapors may rst be passed through a chamber 49 (conventionally shown) containing an adsorptive clay or the like for the separation of any remaining traces of aluminum chloride. The resulting condensate is collected in accumulator D provided with valved vvent line 52.

This isobutane condensate is withdrawn from accumulatorll through line 53 by means of pump 54, which forces it through heat exchanger 56, wherein the 'condensate ispartially vaporized. Sufficient heat is supplied in exchanger 56 to insure the vaporization of at least all of the hydrogen chloride. The partly vaporized condensate is introduced .through line 51 into stripping tower 58, whereinl conditions are so maintained that the hydrogen chloride is substantially entirely stripped from the isobutane product. Tower 58 is desirably operated at a superatmospheric pressure in the range of 450 lbs. per sq. in. and at a charge temperature ofabout 190 F. This isobutane product is removed substantially free of hydrogen chloride through bottoms line 60 and may be subjected to suitable fractionation for the separation and recovery of the isobutane; or, where the isomerization unit is used in conjunction with an alkylation unit, such product may be passed directly to the alkylationreactors. Heat -for the stripping action in tower 58 may be provided by passing a portion of the ybottoms stream through reboiler 62 as by stripper I8 and is removed along with the butane charge vapors through line 20.

Stripper |8 is also provided with a suitable packing material means of lines 63 and 64. The overhead from 18, over which the vsludge trickles downwardly in contact with the rising' butane vapors. These vapors strip out the aluminum chloride which is entrained in the sludge, and the temperature in stripper |8 is maintained sufliciently high so that substantially all of the aluminum chloride is stripped out of the sludge by reason of its sublimation characteristic. As (previously noted, the

butane charge vapors containing the stripped aluminum chloride are removed through line 28 and are passed to reactors 22 and 23. It will lthus be seen that this procedure prevents undue loss of thel aluminum chloride catalyst in the sludge, which is thendischarged from the system for disposal as waste.

The complex aluminumchloride-hydrocarbon sludge, free of entrained aluminum chloride, collects in the bottom of stripper i8, from which a portion is passed through line 36 to scrubber 3| for the purpose of scrubbing entrained and vaporized aluminum chloride from the isobutane product vapors. Desirably, the temperature in scrubber 3| is maintained suflciently low so that an eiective scrubbing action is accomplished. The ilow of the sludge through line 36 is governed by valve 80, which is operated by the level of the sludge in the top of stripper i8. Preferably, this sludge level is maintained above .the top of the packing 18 vso that an eiective contact between the sludge and the butane vapors is continuously obtained. The balance of the substantially aluminum chloride-free sludge is discharged from stripper i8 and from the system through line 82, The ow through `this line is controlled by valve 84, the position of which is governed by the level of the slud-ge in sludge pot 4|).

It will be apparentthat certain changes can the scope of my invention.

of jet pump 14; and, in such case, all the hydrogen chloride is recycled through line 24 from line 12. The use of a jet pump or the like has certain advantages, however; for the difference in the operating pressures maintained in stripping tower 58 and in reactors 22 and 23, the. former of which is operated at a considerably higher pressure than the latter, may then be utilized. Stripper I8 and scrubber 3| are conveniently maintained at`substantially the same pressure under which the reactors are operated. If desirable or necessary, all the recycled hydrogenchloride may bepassed through jet pump-14. In addition, all of the incoming butane charge vapors may be passed directly through line I6 to stripper I8 to act as the stripping medium. Furthermore, although I'have shown stripper I8 The,

and scrubber Il as being fabricated in a single unit, these two towers may be constructed separately; in the arrangement shown, however, no pump is needed in line 36.

It will be apparent that the advantages oi my invention are two-told. vNot only do I provide for the separationoi the entrained aluminum chloride from the isobutane product vapors, but I also provide for the recovery of still active aluminum chloride catalyst entrained in the com-- aluminum chloride wherein vaporous aluminum chloride is carried oil with the reaction product -vapors and wherein still active aluminum chloride is entrained in the complex sludge that is formed. Such reactions include other isomerization 'reactions such as'the conversion of normal pentane to isopentane or the conversion oi' a predominantly straight-chain, low octane number naphtha to a branched-chain naphtha oi a higher antiknock rating, allqrlation reactions such as the alkylation of isobutane with a butylene or' the alkylation of lsopentane with propylene to form a highly isoparaillnic motor fuel' of -high antiknock value, polymerization reactions such as the polymerization of normally gaseous oleflns to gasoline, and the like. f

Furthermore, particularly in the startingup of my process, a complex aluminum chloridehydrocarbon sludge vderived from any suitable source may be used as the scrubbing medium in scrubber 3l. Such sludge may be obtained, for example, from the reaction between olefinic hydrocarbons and aluminum chloride'.

While I have described a preferred form ot embodiment of my invention, I am aware that modifications may be made thereto; therefore,

only such limitations as appear in the claims appended hereinafter should be imposed.

I claim:

i. In the catalytic vapor phase conversion ofA hydrocarbons in the presence of anhydrous aluminum chloride wherein the hydrocarbon vapors to be reacted are passed in contact with the aluminum chloride and the aluminum chloride gradually vaporizes under the conditions of operation,

the steps of recovering the aluminum chloride vapors from the reaction product vapors which comprise countercurrently contacting the reaction product vapors with a complex aluminum chloride-hydrocarbon sludge to substantially scrub the aluminumchloride vapors therefrom.' then countercurrently contacting the sludge ccn- ,taining the scrubbed aluminum chloride with incoming hydrocarbon charge vapors to substan's ually strip the aluminum ehloride'thereirn.

-asoaeeo lually vaporizes under the conditions of operation, the steps o! recovering the aluminum chloride vapors from the reaction product vapors which comprise countercurrently contacting the reaction product vapors with a complex aluminum chloride-hydrocarbon sludge toA substantially scrub the aluminum chloride vapors therefrom, then countcrcurrenthr contacting the sludge containing the scrubbed aluminum chloride with incoming hydrocarboncharge vapors' to substantially strip the aluminum chloride therefrom, passing the hydrocarbon vapors containing the stripped aluminum chloride to the catalytic reaction, and recycling the sludge sub stantially free of aluminum chloride to the scrubbing step.

3. In the isomerization ot normal butane to isobutane in the presence oi anhydrous aluminum chloride and hydrogen chloride gas wherein normal butane vapors admixed`with the hydrogen chloride are passed in contact with the aluminum chloride and the aluminum chloride gradually vapcrizes under the conditions of operation, the steps of recovering'the aluminum chloride vapors from the isobutane product vapors which comprise countercurrently contacting the isobutane product vapors with a complex aluminum chloride-hydrocarbon sludge to substantially scrubthe aluminum chloride vapors therefrom, then countercurrently contacting the sludge containing the. scrubbed aluminum chloride with incoming normal butane charge vapors to substantially lstrip the aluminum chloride therefrom, passing the normall butane4 vapors containing the stripped. aluminum chloride to the catalytic isomerization, returning the sludge substantially free of aluminum chloride to the scrubbing step by gravity, fractionating the isobutane product vapors'substantially free of aluminum chloride at a higher pressure than that maintained on the stripping step to separate the hydrogen chloride gas therefrom, and utilizing this high pressure hydrogen chloride gas to move the sludge from the scrubbing step to the stripping step.

4. In the isomerization of paraiilnc hydrocarbons in vthe presence oi solid anhydrous aluminum chloride wherein hydrocarbon vapors to be isomerized are passed in contact with the aluminum chloride and wherein thev aluminum chloride gradually vaporizes under the conditions of operation and wherein a complex aluminum chloride-hydrocarbon sludge is formed and aluminum 'chloride is entrained by this sludge..

the'ste'ps ot recovering the vaporized and entrained aluminum chloride which comprises Vcountercurrently contacting the sludge with incoming hydrocarbon charge vapors to substan- "-tially strip the entrained aluminum chloride passing the hydrocarbon vapors containing the stripped aluminum chloride to the catalytic reaction.

2. In the catalytic vaporA phase conversion of hydrocarbons in the presence of anhydrous aluminum chloride wherein the hydrocarbon vapors to be reacted are passed in contact with the aluminum chloride and the aluminum chloride grad aluminum chloride and hydrogen chloride gas therefrom. passing such hydrocarbon `varuirs containing the stripped aluminum chloride'to the=catalytic isomer-lation, 'passing-sludge sub- -stantially ireeoi'entrained aluminum-chloride -incovunterem-rentcontactwiththeisomerln'tien,

product vapors to scrub the aluminum chloride vapors therefrom. returning sludge containing the scrubbed aluminum -chloride 'to the sttiplns and from the system the excess sludge substantially free o! entrained aluminum chloride.

5. In the isomerization of normal butane to isobutane in the presence of solid anhydrous wherein normal butane vapors admixed with the hydrogen chloride are passed in contact with substantially free of entrained aluminum chloride to substantially scrub the aluminum chloride vapors therefrom, passing sludge from the stripping step to the scrubbing step by gravity, eliminating from the system the excess sludge substantially free of entrained aluminum chlovtacting the isobutane product vapors with sludge ride, combining the sludge from the scrubbing step with the sludge from the catalytic isomerization, fractionating the isobutane product vapors substantially free of aluminum chloride at a pressure higher than that maintained on the stripping step to separate the hydrogen chloride gas therefrom, and utilizing this high pressure hydrogen chloride gas to move the combined sludge to the stripping step.

6. 'I'he method as claimed in claim 5, which includes .dividing the incoming normal butane charge vapors and passing one portion thereof directly to the catalytic isomerization.

'7. The method as claimed `in`claim 5, which I includes dividing the separated hydrogen chloride gas into two portions and recycling one portion thereof directly to the catalytic isomeriza-l tion.

8. The method as claimed in claim 5, which includes conducting the stripping and scrubbing steps in packed columns and maintaining the upper level ,of the sludge above the top of the packing in each column.

9. In a catalytic vapor phase hydrocarbon conversion process employing an aluminum halide catalyst and producing vaporous conversion products and also producing a sludge and wherein said catalyst is subject to vaporization and removal with the conversion products and is also subject to entrainment by said sludge and removal therewith, the steps for recovering the catalyst so removed with the conversion products and with the sludge', comprising passing incoming hydrocarbon charge vapors in contact with the removed sludge to strip the entrained catalyst from the sludge, passing said vapors bearing the. catalyst stripped from the sludge to the conversion, subsequently passing the Vaporous conversion productsI in contact with said sludge from which the catalyst has been stripped to scrub the catalyst from said products, and employing in said stripping step the sludge bearing the catalyst so scrubbed from the conversion products.

10. In a continuous catalytic vapor phase hydrocarbon conversion process employing an aluminum halide catalyst and producing vaporous conversion products and also producing a sludge and wherein said catalyst is subject to vaporization and removal with the conversion products and is also subject to entrainment by said sludge and removal therewith, the steps for recovering the catalyst so removed, with the conversion products and with the sludge, comprising continuously passing the removed sludge through a packed stripping zone, continuously passing incoming hydrocarbon charge vapors in contact with the sludge Within the stripping zone tostrip the entrained catalystfrom the sludge, continuously passing said vapors bearing the catalyst scrubbing zone, continuously passing the .vaporous conversion products through a packed scrubbing zone and in contact therein with said sludge from which the catalyst has been stripped 'to scrub the catalyst from said products. and continuously passing the sludge bearing the catalyst.

, so scrubbed from the conversion products from the scrubbing zone to the stripping zone 'for use in said stripping step.'

UTAH TSAO. 

